Resins for resists and chemically amplifiable resist compositions

ABSTRACT

A resist resin containing a monomer unit selected from the group consisting of the following Formulas (I) and (II):  
                 
 
     wherein each of R 1  and R 2  represents a hydrogen atom, alkyl group or acid-deprotectable protecting group respectively, and  
                 
 
     wherein a substituent R 3  represents an alkyl group, or a functional group comprising an acid-deprotectable protecting group, m representing the number of R 3  is 0 (non-substitution), 1, 2 or more, R 3  may be different from each other, provided that m is 2 or more, and n represents an integer of 0 to 4, has no rough spots on the surface after etching and so has good dry etching resistance, and therefore the resist resin is preferably used as a photo resist for DUV.

TECHNICAL FIELD

[0001] The present invention relates to a resist resin and a chemicallyamplified resist composition, and the present invention particularlyrelates to a resist resin and a chemically amplified resist composition,which are preferably used in a microfabrication using an excimer laseror electron beam.

BACKGROUND ART

[0002] In recent years, a miniaturization has quickly been progressed bythe development of a lithographic technique in the field ofmicrofabrication for production of semiconductor devices or liquidcrystal devices. As such a microfabrication technique, the conversion ofan exposure source into a source with a short wavelength has generallybeen used. Specifically, previous ultraviolet rays including g-line andi-line as a typical example have been changed to DUV.

[0003] Presently, a KrF excimer laser (248 nm) lithographic techniquehas been introduced in the market, and an ArF excimer laser (193 nm)lithographic technique, which is directed towards the conversion of anexposure source into that with a further shorter wavelength, is beingintroduced. Moreover, an F₂ excimer laser (157 nm) lithographictechnique is being studied as a technique for the next generation.Furthermore, an electron beam lithographic technique, which somewhatdiffers from the above techniques, is also intensively being studied.

[0004] As a resist with high resolution for such a light source with ashort wavelength or electron beam, a “chemically amplified resist” hasbeen proposed by International Business Machine (IBM) Corporation, andat present, the improvement and development of this chemically amplifiedresist has vigorously been progressing.

[0005] Resins used for resist are also forced to change their structurewith the conversion of an exposure source into that with a shortwavelength. In the KrF excimer laser lithography, employed ispolyhydroxystyrene or polyhydroxystyrene with its hydroxyl groupprotected with an acid-deprotectable solubility-inhibiting group that ishighly transparent to the light at 248 nm. In the ArF excimer laserlithography, it is almost impossible to use the above resin due toinsufficient transparency to the light at 193 nm. Accordingly, acrylresins and cycloolefin resins transparent to the light at 193 nm attractattention. Examples of acryl resins include those described in JapanesePatent Laid-Open Nos. 4-39665, 10-207069 and others, and examples ofcycloolefin resins include those described in Japanese Patent Laid-OpenNo. 10-153864 and others.

[0006] However, these resins are still insufficient in theirperformances, and further higher dry etching resistance is required.

[0007] As a photoresist for the ArF excimer laser, Japanese PatentLaid-Open No. 11-212265 describes a resin comprising a monomer unitderived from 2-alkyl-2-adamantyl (meth)acrylate and a monomer unitderived from itaconic anhydride, and Japanese Patent Laid-Open No.2000-26446 describes a resin obtained by (co)polymerization of(meth)acrylate derivatives having polycyclic lactone groups. Thesepublications describe that these resins are excellent in an adhesiveproperty to a substrate and etching resistance, but these are irrelevantto the feature of the present invention.

DISCLOSURE OF THE INVENTION

[0008] Accordingly, it is an object of the present invention to providea resist resin and a chemically amplified resist composition, which havehigh dry etching resistance and are preferably used in DUV excimer laserlithography or electron beam lithography.

[0009] The present inventors have intensively studied on the structureof a resist resin to achieve the above object, they have found that aresist resin and a chemically amplified resist composition, which arepreferably used in DUV excimer laser lithography or electron beamlithography, can be obtained by using a resin having a specificstructure, thereby completing the present invention.

[0010] That is to say, the present invention relates to a resist resincapable of being solubilized in an alkaline solution by the action of anacid, characterized by comprising at least one type of monomer unitselected from the group consisting of monomer units represented by thefollowing Formulas (I) and (II):

[0011] wherein each of R¹ and R² represents a hydrogen atom, alkyl groupor acid-deprotectable protecting group, and

[0012] wherein a substituent R³ represents an alkyl group, or afunctional group comprising an acid-deprotectable protecting group, mrepresenting the number of R³ is 0 (non-substitution), 1, 2 or more, R³may be different from each other, provided that m is 2 or more, and nrepresents an integer of 0 to 4.

[0013] Moreover, the chemically amplified resist composition of thepresent invention comprises this resist resin and a photo acidgenerator.

[0014] Furthermore, the method of forming a pattern of the presentinvention comprises a step of applying this chemically amplified resistcomposition on a substrate to be processed, an exposure step and adeveloping step.

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The present invention will be explained in detail below.

[0016] The resist resin of the present invention is capable of beingsolubilized in an alkaline solution by the action of an acid, andcomprises at least one type of monomer unit selected from the groupconsisting of monomer units represented by the above described Formulas(I) and (II). These monomer units are contained preferably at 0.5 to 40mole %, and particularly preferably at 1 to 20 mole % in the resin.

[0017] In the above described Formula (I), each of R¹ and R² representsa hydrogen atom, alkyl group or acid-deprotectable protecting group.This alkyl group preferably contains 1 to 13 carbon atoms. Theacid-deprotectable protecting group means a protecting group which iscapable of giving rise to decomposition thereof by the action of anacid, and examples of such a group include a t-butyl group, atetrahydropyran-2-yl group, a tetrahydrofuran-2-yl group, a4-methoxytetrahydropyran-4-yl group, a 1-ethoxyethyl group, a1-butoxyethyl group, a 1-propoxyethyl group, a 3-oxocyclohexyl group, a2-methyl-2-adamantyl group, a 2-ethyl-2-adamantyl group, a8-methyl-8-tricyclodecyl group, a 1,2,7,7-tetramethyl-2-norbonyl group,a 2-acetoxymenthyl group, a 2-hydroxymenthyl group, a1-methyl-1-cyclohexylethyl group and others.

[0018] In the above described Formula (II), a substituent R³ representsone, two or more hydrogen atom(s), alkyl group(s), or functionalgroup(s) comprising acid-deprotectable protecting group(s). This alkylgroup preferably contains 1 to 13 carbon atoms. Examples of thefunctional group comprising an acid-deprotectable protecting groupinclude a t-butoxy group, a tetrahydropyran-2-yloxy group, a1-butoxyethyloxy group, a 2-methyl-2-adamantyloxy group, amenthoxyacetyloxy group, a t-butoxycarbonyl group, a2-methyl-2-adamantyloxycarbonyl group and others. The n in the abovedescribed Formula (II) represents an integer of 0 to 4, and preferably 1to 3. The substituent R³ binds to a methylene carbon constituting alactone ring, and m, the number of the substituent R³, is 0, 1, 2 ormore. When m is 0, R³ does not exist, and it indicates that a hydrogenatom on a methylene carbon is not substituted. The upper limit of m is2+2n. When m is 2 or more, R³ may be different from one another.Further, two hydrogen atoms on a single methylene carbon may besubstituted by R³. The m is preferably 1 to 2.

[0019] The present inventors have found that the direct introduction ofcyclic skeletons represented by the above Formulas (I) and (II) into amain chain enables to improve dry etching resistance, and thereby roughspots appearing on the surface of a resist after dry etching arereduced.

[0020] The monomer unit of the above described Formula (I) can becontained in the resin by (co)polymerization of monomers such as

[0021] di(methyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0022] di(ethyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0023] di(propyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0024] di(isopropyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0025] di(butyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0026] di(isobutyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0027] di(t-butyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0028] di(t-amyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0029] di(cyclohexyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0030] di(isobornyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0031] di(adamantyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0032] di(2-methyladamantyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,di(tricyclodecanyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0033] di(tetrahydropyranyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,di(dicyclopentadienyl)-2,2′-[oxybis(methylene)]bis-2-propenoate andothers.

[0034] Preferred monomers are

[0035] di(t-butyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,

[0036] di(2-methyladamantyl)-2,2′-[oxybis(methylene)]bis-2-propenoate,and

[0037] di(tricyclodecanyl)-2,2′-[oxybis(methylene)]bis-2-propenoate.

[0038] The monomer unit of the above described Formula (II) can becontained in the resin by the (co)polymerization of monomers such as2-methylene-3-propanolide, 2-methylene-5-pentanolide,2-methylene-6-hexanolide, 2-methylene-7-heptanolide,2-methylene-butyrolactone, 4-methyl-2-methylene butyrolactone,4-ethyl-2-methylene butyrolactone,2-methylene-4,4-dimethyl-γ-butyrolactone and others. Preferred monomersare 2-methylene-butyrolactone, 4-methyl-2-methylene butyrolactone,4-ethyl-2-methylene butyrolactone, and2-methylene-4,4-dimethyl-γ-butyrolactone.

[0039] To the resist resin of the present invention, a structure havinga functional group which is easily eliminated by the action of acid anda structure having high dry etching resistance are preferablyintroduced. Examples of other monomer units used to introduce suchstructures include units for resins which have been known to be used forchemically amplified resist compositions. These units are selected asappropriate depending on the type of a light source used in lithography.

[0040] For example, when the KrF excimer laser or electron beam is usedas a light source, taking the high etching resistance intoconsideration, a resin obtained by copolymerization of p-hydroxystyreneor a derivative thereof is preferably used. In such a case, it isessential that the copolymer has, in its structure, a functional groupwhich is eliminated by the action of an acid, allowing solubilization inan alkaline developing solution, so that the copolymer is used as achemically amplified resist composition.

[0041] Specifically, it is preferable that the hydroxyl group ofp-hydroxystyrene or the carboxyl group of a monomer to be copolymerizedis protected by an acetoxy group, t-butyl group, tetrahydropyranylgroup, methyladamantyl group or the like.

[0042] When the ArF excimer laser is used as a light source, since thewavelength of the laser is short, a resin obtained by copolymerizingp-hydroxystyrene or a derivative thereof cannot be used because of itslow light transmittance. Therefore, taking into consideration balancewith etching resistance, a resin having an alicyclic skeleton ispreferable.

[0043] Specific examples of such a resin include the acryl resindescribed in Japanese Patent Laid-Open No. 9-090637 or 10-207069, andthe olefin resins described in Japanese Patent Laid-Open No. 10-207070or 10-218941.

[0044] Of these, acrylic copolymers obtained by polymerizing a monomerhaving an alicyclic skeleton and a monomer having a lactone skeleton areparticularly preferable as a resin for the ArF excimer laserlithography. The monomer unit having an alicyclic skeleton is containedin the resin preferably at 10 to 90 mole %, and particularly preferablyat 30 to 60 mole %. The monomer unit having a lactone skeleton iscontained in the resin preferably at 10 to 90 mole %, and particularlypreferably at 40 to 70 mole %. It should be noted that the simpledescription “monomer having a lactone skeleton” is used in the presentspecification to mean that it does not include the monomer unit ofFormula (II).

[0045] A monomer having an alicyclic skeleton imparts high dry etchingresistance to a copolymer obtained by polymerization and a resincomposition thereof, and particularly, a monomer containing a protectinggroup which is eliminated by the action of an acid can impart highsensitivity to a copolymer and a resin composition thereof used in alithography using a laser of 193 nm. The monomer having an alicyclicskeleton can be used singly or in combination of two or more types, asnecessary.

[0046] Such a monomer having an alicyclic skeleton is preferably atleast one type selected from the group consisting of cyclohexyl(meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate,tricyclodecanyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, andderivatives having substituents such as an alkyl group, a hydroxylgroup, a carboxyl group and others on the alicyclic rings of thesemonomers. Specific examples include 1-isobonyl methacrylate,2-methacryloyloxy-2-methyladamantane, cyclohexyl methacrylate, adamantylmethacrylate, tricyclodecanyl methacrylate, dicyclopentadienylmethacrylate and others.

[0047] A monomer having a lactone skeleton imparts a property ofadhering to a substrate to a copolymer obtained by polymerization and aresin composition thereof, and particularly, a monomer containing aprotecting group which is eliminated by the action of an acid can imparthigh sensitivity to a copolymer and a resin composition thereof used ina lithography using a laser of 193 nm. The monomer having a lactoneskeleton can be used singly or in combination of two or more types, asnecessary.

[0048] Such a monomer having a lactone skeleton is preferably at leastone type selected from the group consisting of (meth)acrylate having aδ-valerolactone ring, (meth)acrylate having a γ-butyrolactone ring, andderivatives having substituents such as an alkyl group, a hydroxylgroup, a carboxyl group and others on the lactone rings of thesemonomers.

[0049] Specific examples includeβ-methacryloyloxy-β-methyl-δ-valerolactone,β-methacryloyloxy-γ-butyrolactone,β-methacryloyloxy-β-methyl-γ-butyrolactone,α-methacryloyloxy-γ-butyrolactone,2-(1-methacryloyloxy)ethyl-4-butanolide, pantolactone methacrylate andothers.

[0050] Moreover, when a resist resin is required to have further higherdry etching resistance, a monomer having a polycyclic lactone ring ispreferable as the above described monomer having a lactone skeleton. Theterm polycyclic lactone ring is used to mean a structure in which alactone ring is introduced into a polycyclic skeleton such as anisobornyl skeleton, adamantane skeleton, tricyclodecanyl skeleton ordicyclopentadienyl skeleton. As a monomer having a polycyclic lactonering, (meth)acrylate having such a polycyclic lactone ring or the likeis preferable.

[0051] Specific examples include5-methacryloyloxy-6-hydroxybicyclo[2,2,1]heptane-2-carboxylic-6-lactone,5-acryloyloxy-6-hydroxybicyclo[2,2,1]heptane-2-carboxylic-6-lactone,2-methyl-6-methacryloyloxy-6-hydroxybicyclo[2,2,1]heptane-2-carboxylic-6-lactone,2-methyl-6-acryloyloxy-6-hydroxybicyclo[2,2,1]heptane-2-carboxylic-6-lactone,and others.

[0052] The weight-average molecular weight of this resist resin is notparticularly limited, but it is preferably within a range of 1,000 to100,000. As the weight-average molecular weight increases larger, dryetching resistance is improved and thereby the form of the resistpattern becomes better. In contrast, as the weight-average molecularweight decreases, solubility to a resist solvent is improved andresolution is improved.

[0053] A simple and preferred method of producing this resist resin is,for example, what is called a drop polymerization method in which amonomer solution obtained by previously dissolving a monomer and apolymerization initiator in an organic solvent, is dropped in an organicsolvent kept at a constant temperature.

[0054] An organic solvent used in the drop polymerization method is notparticularly limited, but a solvent in which both a monomer and theobtained copolymer can be dissolved is preferable, and examples of suchan organic solvent include 1,4-dioxane, isopropyl alcohol, acetone,tetrahydrofuran and others.

[0055] A polymerization initiator used in the drop polymerization methodis not particularly limited, and examples of such a polymerizationinitiator include azo compounds such as azobisisobutyronitrile and2,2′-azobis(2,4-dimethylvaleronitrile), organic peroxides such asbenzoyl peroxide, and others. Moreover, mercaptans such as n-butylmercaptan and n-octyl mercaptan may be used in combination as chaintransfer agents.

[0056] A polymerization temperature in the drop polymerization method isnot particularly limited, but the temperature is preferably within arange of 50° C. to 150° C. A dropping time is not particularly limited,but generally the time is 6 hours or longer. It is further preferablethat the temperature is kept constant for about 2 hours after completionof dropping to complete polymerization.

[0057] A solution of resin solubilized in an alkaline solution by acid,which is produced by the drop polymerization method, is diluted with agood solvent such as tetrahydrofuran or 1,4-dioxane, so that thesolution has an appropriate viscosity. Thereafter, the solution isdropped in a large amount of a poor solvent such as heptane, methanol orwater for deposition. Thereafter, the deposit is filtrated off and fullydried. This step is called reprecipitation, and it is unnecessary insome cases. However, this step is extremely effective to remove anunreacted monomer remaining in the polymerization solution, apolymerization initiator and the like. If these unreacted productsremain as are in the solution, these have a possibility of exerting anadverse effect on the performances of a resist. Accordingly, it ispreferable to remove these unreacted products.

[0058] The chemically amplified resist composition of the presentinvention at least comprises the above described resist resin and aphotoacid generator. Moreover, when the chemically amplified resistcomposition is applied on a substrate to be processed, it is dissolvedin a solvent and used as a solution. This solvent is appropriatelyselected depending on purposes. The selection of the solvent is carriedout, taking into consideration conditions other than the solubility of aresin, such as homogeneity of a coating film, appearance, safety andothers.

[0059] Examples of a solvent meeting these conditions include: linearketones such as 2-pentanone and 2-hexanone; cyclic ketones such ascyclopentanone and cyclohexanone; propylene glycol monoalkyl etheracetates such as propylene glycol monomethyl ether acetate and propyleneglycol monoethyl ether acetate; ethylene glycol monoalkyl ether acetatessuch as ethylene glycol monomethyl ether acetate and ethylene glycolmonoethyl ether acetate; propylene glycol monoalkyl ethers such aspropylene glycol monomethyl ether and propylene glycol monoethyl ether;ethylene glycol monoalkyl ethers such as ethylene glycol monomethylether and ethylene glycol monoethyl ether; diethylene glycol alkylethers such as diethylene glycol dimethyl ether and diethylene glycoldiethyl ether; esters such as ethyl acetate and ethyl lactate; alcoholssuch as cyclohexanol and 1-octanol; ethylene carbonate; γ-butyrolactone;and others. These solvents can be used singly or in combination of twoor more types. The amount of a solvent used is not particularly limitedas long as it is an amount capable of dissolving a resin.

[0060] A photo acid generator can appropriately be selected from amongacid generators which can be used as those for the chemically amplifiedresist composition. The photoacid generator can be used singly or incombination of two or more types.

[0061] Specific examples of such a photoacid generator include an oniumsalt compound, a sulfone imide compound, a sulfone compound, a sulfonatecompound, a quinone diazide compound, a diazo methane compound andothers. Of these, an onium salt compound is preferable, and examples ofsuch an onium salt compound include a sulfonium salt, an iodonium salt,a phosphonium salt, a diazonium salt, a pyridinium salt and others.

[0062] Specific examples include triphenylsulfonium triflate,triphenylsulfonium hexafluoroantimonate, triphenylsulfoniumnaphthalenesulfonate, (hydroxyphenyl)benzylmethylsulfoniumtoluenesulfonate, diphenyliodonium triflate, diphenyliodoniumpyrenesulfonate, diphenyliodonium dodecylbenzenesulfonate,diphenyliodonium hexafluoroantimonate and others.

[0063] The amount of a photo acid generator used is appropriatelydetermined depending on the type of the photo acid generator used, butthe amount is generally 0.1 to 20 parts by weight, and preferably 0.5 to10 parts by weight with respect to 100 parts by weight of resist resin.When the amount of a photoacid generator used is too small, there is arisk that it might be difficult to fully carry out a chemical reactionby the catalytic action of acid generated by exposure. On the otherhand, when the amount is too large, there is another risk that thestability of a resist composition might be decreased, unevenness mightbe generated when the composition is applied, or that scum or the likemight be generated in a developing step.

[0064] The chemically amplified resist composition of the presentinvention further comprises various additives such as a surfactant, aquencher, a sensitizer, an antihalation agent, a preservative stabilizeror an antifoaming agent, as necessary.

[0065] Examples of a surfactant include nonion surfactants such aspolyoxyethylene lauryl ether and polyethylene glycol dilaurate, as wellas surfactants known as the following trade names such as Polyflow No.75 (produced by Kyoeisha Chemical Co., Ltd.), Megafac F173 (produced byDainippon Ink and Chemicals Incorporated), Surflon SC-105 (produced byAsahi Glass Co., Ltd.), L-70001 (produced by Shin-Etsu Chemical Co.,Ltd.) and others.

[0066] In a method of forming a pattern which uses such a chemicallyamplified resist composition, deep UV having a wavelength of 260 nm orshorter (e.g. the KrF excimer laser beam, the ArF excimer laser beam andthe F₂ excimer laser beam) and an electron beam can be used as exposuresources, and therefore the chemically amplified resist composition canpreferably be used in microfabrication of semiconductor substrates suchas a silicon wafer. A coating step, an exposure step, a developing stepand the like in the pattern formation method can be carried out by knownmethods.

EXAMPLES

[0067] The present invention will further be explained in the followingexamples. The term “part” is herein used to mean “part by weight”,unless otherwise specified.

[0068] The measurement of physical properties of a copolymer and theevaluation of a resist were carried out by the following methods.

[0069] <Weight-Average Molecular Weight>

[0070] The weight-average molecular weight of a resist resin wasdetermined by gel permeation chromatography (GPC) and using polymethylmethacrylate as reference. Chloroform or tetrahydrofuran was used as asolvent.

[0071] <Average Copolymer Composition of Copolymers (Mole %)>

[0072] The average copolymer composition of a copolymer was obtained by¹H-NMR measurement. Heavy chloroform or heavy acetone was used as asolvent.

[0073] <Sensitivity>

[0074] Post-exposure baking was carried out immediately after a resistfilm formed on a silicon wafer was subjected to exposure, and then theresist film was developed in an alkaline developing solution, washedwith water and dried, so that a resist pattern was formed. Sensitivitywas defined as a light exposure forming a line-and-space pattern(L/S=1/1) at a line width of 1/1.

[0075] <Resolution>

[0076] Resolution is defined as the minimal dimension (μm) of a resistpattern which is formed when exposure is carried out at theabove-described light exposure.

[0077] <Dry Etching Resistance>

[0078] A resist film formed on a silicon wafer was subjected to etching,and the etching rate of each resist was measured by a reduction inthickness of individual films (normalized by setting the etching rate ofa novolac resin as 1). Etching was carried out employing an etchapparatus produced by Tokyo Electron Ltd., using C₄F₈/Ar/O₂ mixed gas,under etching conditions at 2,000 W, at 50 mTorr, for 50 seconds.

[0079] The surface of a resist was observed with an electron microscopeafter etching, and a resist having no unevenness on the surface wasevaluated with a mark of “◯” and a resist having unevenness androughness on the surface was evaluated with a mark of “×”.

Synthesis Example 1

[0080] Twenty parts of 1,4-dioxane was placed in a flask equipped with anitrogen introduction port, an agitator, a condenser and a thermometerin a nitrogen atmosphere, and the temperature of a hot water bath wasraised to 80° C. with stirring. A monomer solution obtained by mixing22.0 parts of p-t-butoxystyrene (abbreviated as PTBST, molecular weight:176), 13.5 parts of p-hydroxystyrene (abbreviated as HS, molecularweight: 120), 3.7 parts ofdi(t-butyl)-2,2′-[oxybis(methylene)]bis-2-propenoate (abbreviated asTBED, molecular weight: 298), 62.5 parts of 1,4-dioxane and 1.9 parts ofazobisisobutyronitrile was dropped in the flask at a constant rate over6 hours, and then the temperature of 80° C. was kept for 2 hours.Thereafter, the obtained reaction solution was diluted approximatelytwice with tetrahydrofuran, and while stirring, the obtained dilutedsolution was dropped in water in an amount about 10 times the amount ofthe diluted solution so as to obtain a white precipitate (copolymerA-1). The obtained precipitate was filtrated off and then dried under areduced pressure at 60° C. for approximately 40 hours.

[0081] Subsequently, the physical properties of the obtained copolymerA-1 were measured. The weight-average molecular weight was 9,500 and thecomposition ratio of the copolymer was PTBST/HS/TBED=50/45/5 mole %.

Synthesis Example 2

[0082] Synthesis was carried out in the same manner as in Synthesisexample 1 with the exception that 1.6 parts of2-methylene-4,4-dimethyl-γ-butyrolactone (abbreviated as MDMBL,molecular weight: 126) was used instead of 3.7 parts ofdi(t-butyl)-2,2′-[oxybis(methylene)]bis-2-propenoate (abbreviated asTBED, molecular weight: 298), so that copolymer A-2 was obtained.

[0083] Subsequently, the physical properties of the obtained copolymerA-2 were measured. The weight-average molecular weight was 9,400 and thecomposition ratio of the copolymer was PTBST/HS/MDMBL=50/45/5 mole %.

Synthesis Example 3

[0084] Twenty parts of 1,4-dioxane was placed in a flask equipped with anitrogen introduction port, an agitator, a condenser and a thermometerin a nitrogen atmosphere, and the temperature of a hot water bath wasraised to 80° C. with stirring. A monomer solution obtained by mixing29.3 parts of 2-methacryloyloxy-2-methyladamantane (abbreviated asMAdMA, molecular weight: 234), 19.1 parts ofβ-methacryloyloxy-γ-butyrolactone (abbreviated as HGBMA, molecularweight: 170), 3.7 parts ofdi(t-butyl)-2,2′-[oxybis(methylene)]bis-2-propenoate (abbreviated asTBED, molecular weight: 298), 62.5 parts of 1,4-dioxane and 1.9 parts ofazobisisobutyronitrile was dropped in the flask at a constant rate over6 hours, and then the temperature of 80° C. was kept for 2 hours.Thereafter, the obtained reaction solution was diluted approximatelytwice with tetrahydrofuran, and while stirring, the obtained dilutedsolution was dropped in methanol in amount about 10 times the amount ofthe diluted solution so as to obtain a white precipitate (copolymerA-3). The obtained precipitate was filtrated off and then dried under areduced pressure at 60° C. for approximately 40 hours.

[0085] Subsequently, the physical properties of the obtained copolymerA-3 were measured. The weight-average molecular weight was 9,500 and thecomposition ratio of the copolymer was MAdMA/HGBMA/TBED=50/45/5 mole %.

Synthesis Example 4

[0086] Synthesis was carried out in the same manner as in Synthesisexample 3 with the exception that 1.6 parts of2-methylene-4,4-dimethyl-γ-butyrolactone (abbreviated as MDMBL,molecular weight: 126) was used instead of 3.7 parts ofdi(t-butyl)-2,2′-[oxybis(methylene)]bis-2-propenoate (abbreviated asTBED, molecular weight: 298), so that copolymer A-4 was obtained.

[0087] Subsequently, the physical properties of the obtained copolymerA-4 were measured. The weight-average molecular weight was 9,500 and thecomposition ratio of the copolymer was MAdMA/HGBMA/MDMBL=50/45/5 mole %.

Synthesis Example 5

[0088] Twenty parts of acetonitrile was placed in a flask equipped witha nitrogen introduction port, an agitator, a condenser and a thermometerin a nitrogen atmosphere, and the temperature of a hot water bath wasraised to 80° C. with stirring. A monomer solution obtained by mixing29.3 parts of 2-methacryloyloxy-2-methyladamantane (abbreviated asMAdMA, molecular weight: 234), 24.9 parts of5-methacryloyloxy-6-hydroxybicyclo[2,2,1]heptane-2-carboxylic-6-lactone(abbreviated as HBHMA, molecular weight: 222), 1.6 parts of2-methylene-4,4-dimethyl-γ-butyrolactone (abbreviated as MDMBL,molecular weight: 126), 62.5 parts of acetonitrile and 1.9 parts ofazobisisobutyronitrile was dropped in the flask at a constant rate over6 hours, and then the temperature of 80° C. was kept for 2 hours.Thereafter, the obtained reaction solution was diluted approximatelytwice with acetonitrile, and then, the obtained diluted solution wasdropped in methanol in an amount about 10 times the amount of thediluted solution with stirring so as to obtain a white precipitate(copolymer A-5). The obtained precipitate was filtrated off and thendried under a reduced pressure at 60° C. for approximately 40 hours.

[0089] Subsequently, the physical properties of the obtained copolymerA-5 were measured. The weight-average molecular weight was 11,000 andthe composition ratio of the copolymer was MAdMA/HBHMA/MDMBL=50/45/5mole %.

Comparative Synthesis Example 1

[0090] Twenty parts of 1,4-dioxane was placed in a flask equipped with anitrogen introduction port, an agitator, a condenser and a thermometerin a nitrogen atmosphere, and the temperature of a hot water bath wasraised to 80° C. with stirring. A monomer solution obtained by mixing22.0 parts of p-t-butoxystyrene (abbreviated as PTBST, molecular weight:176), 15.0 parts of p-hydroxystyrene (abbreviated as HS, molecularweight: 120), 62.5 parts of 1,4-dioxane and 1.9 parts ofazobisisobutyronitrile was dropped in the flask at a constant rate over6 hours, and then the temperature of 80° C. was kept for 2 hours.Thereafter, the obtained reaction solution was diluted to approximatelytwice with tetrahydrofuran, and then, the obtained diluted solution wasdropped in water in an amount about 10 times the amount of the dilutedsolution with stirring so as to obtain a white precipitate (copolymerAH-1). The obtained precipitate was filtrated off and then dried under areduced pressure at 60° C. for approximately 40 hours.

[0091] Subsequently, the physical properties of the obtained copolymerAH-1 were measured. The weight-average molecular weight was 12,000 andthe composition ratio of the copolymer was PTBST/HS=51/49 mole %.

Comparative Synthesis Example 2

[0092] Twenty parts of 1,4-dioxane was placed in a flask equipped with anitrogen introduction port, an agitator, a condenser and a thermometerin a nitrogen atmosphere, and the temperature of a hot water bath wasraised to 80° C. with stirring. A monomer solution obtained by mixing29.3 parts of 2-methacryloyloxy-2-methyladamantane (abbreviated asMAdMA, molecular weight: 234), 21.2 parts ofβ-methacryloyloxy-γ-butyrolactone (abbreviated as HGBMA, molecularweight: 170), 62.5 parts of 1,4-dioxane and 1.9 parts ofazobisisobutyronitrile was dropped in the flask at a constant rate over6 hours, and then the temperature of 80° C. was kept for 2 hours.Thereafter, the obtained reaction solution was diluted approximatelytwice with tetrahydrofuran, and then, the obtained diluted solution wasdropped in methanol in an amount about 10 times the amount of thediluted solution with stirring so as to obtain a white precipitate(copolymer AH-2). The obtained precipitate was filtrated off and thendried under a reduced pressure at 60° C. for approximately 40 hours.

[0093] Subsequently, the physical properties of the obtained copolymerAH-2 were measured. The weight-average molecular weight was 11,000 andthe composition ratio of the copolymer was MAdMA/HGBMA=50/50 mole %.

Comparative Synthesis Example 3

[0094] Twenty parts of acetonitrile was placed in a flask equipped witha nitrogen introduction port, an agitator, a condenser and a thermometerin a nitrogen atmosphere, and the temperature of a hot water bath wasraised to 80° C. with stirring. A monomer solution obtained by mixing29.3 parts of 2-methacryloyloxy-2-methyladamantane (abbreviated asMAdMA, molecular weight: 234), 27.8 parts of5-methacryloyloxy-6-hydroxybicyclo[2,2,1]heptane-2-carboxylic-6-lactone(abbreviated as HBHMA, molecular weight: 222), 62.5 parts ofacetonitrile and 1.9 parts of azobisisobutyronitrile was dropped in theflask at a constant rate over 6 hours. During dropping, an insolubleprecipitate was generated in the polymerization solvent. Then, thetemperature of 80° C. was kept for 2 hours. Thereafter, the obtainedheterogeneous reaction solution was diluted approximately twice withacetonitrile, and then, the obtained diluted solution was dropped inmethanol in an amount about 10 times the amount of the diluted solutionwith stirring so as to obtain a white precipitate (copolymer AH-3). Theobtained precipitate was filtrated off and then dried under a reducedpressure at 60° C. for approximately 40 hours.

[0095] Subsequently, the physical properties of the obtained copolymerAH-3 were measured. The weight-average molecular weight was 12,000 andthe composition ratio of the copolymer was MAdMA/HBHMA=52/48 mole %.

Examples 1 to 5 and Comparative Examples 1 to 3

[0096] The ingredients of individual examples and comparative examplesshown in Table 1 were mixed to obtain a homogeneous solution for eachexample or comparative example, and the obtained solution was thenfiltrated through a membrane filter having a pore size of 0.1 μm so asto prepare a resist composition solution. Thereafter, each compositionsolution was spincoated on a silicon wafer, and thereafter, pre-bakingwas carried out using a hot plate at 120° C. for 60 seconds to form aresist film having a film thickness of 0.5 μm. Subsequently, resistfilms of Examples 1 and 2 and Comparative example 1 were exposed usingthe KrF excimer laser exposure equipment, whereas resist films ofExamples 3 to 5 and Comparative example 2 were exposed using the ArFexcimer laser exposure equipment. Then, post-exposure baking was carriedout at 120° C. for 60 seconds using a hot plate. Thereafter, developmentwas carried out at room temperature using a 2.38 weight %tetramethylammonium hydroxide solution followed by washing with purewater and drying, so as to form a resist pattern. The evaluation resultsof the obtained resist patterns are shown in Tables 2 and 3. Moreover,the results obtained by measuring the etching rate of each resist underthe above described conditions are also shown in Tables 2 and 3.

[0097] With regard to the copolymer AH-3 in Comparative synthesisexample 3 (Comparative example 3), the resist solution was intended tobe prepared as mentioned above, but the copolymer did not dissolve inthe solvent, and therefore the resist performances could not beevaluated.

[0098] Thus, in the above examples, sensitivity and resolution were notsignificantly decreased, and dry etching resistance was improved, sothat rough spots were not generated on the surface of a resist afteretching. In contrast, in comparative examples, dry etching resistancewas not sufficient, and so rough spots were generated on the surface ofa resist after etching. TABLE 1 Photo acid Copolymer generator Solvent^((Note 1)) (part) (part) (part) Example 1 A-1 (100) B-1 (2) 500 Example2 A-2 (100) B-1 (2) 500 Example 3 A-3 (100) B-1 (2) 500 Example 4 A-4(100) B-1 (2) 500 Example 5 A-5 (100) B-1 (2) 500 Comparative AH-1 (100)B-1 (2) 500 example 1 Comparative AH-2 (100) B-1 (2) 500 example 2

[0099] TABLE 2 Roughness on Sensitivity Resolution Etching surface after(mJ/cm²) (μm) rate ^((Note 1)) etching ^((Note 2)) Example 1 10.0 0.351.12 ◯ Example 2 12.1 0.36 1.13 ◯ Comparative 10.1 0.35 1.20 X example 1

[0100] TABLE 3 Roughness on Sensitivity Resolution Etching surface after(mJ/cm²) (μm) rate ^((Note 1)) etching ^((Note 2)) Example 3 4.0 0.161.14 ◯ Example 4 4.5 0.17 1.15 ◯ Example 5 5.0 0.17 1.05 ◯ Comparative3.6 0.16 1.26 X example 2

Industrial Applicability

[0101] The resist resin and the chemically amplified resist compositionof the present invention have no rough spots on the resist surface afteretching and have good dry etching resistance as well as high sensibilityand resolution, and accordingly these resist resin and chemicallyamplified resist composition can stably form a high-precision fineresist pattern. Therefore, the resist resin and the chemically amplifiedresist composition of the present invention can preferably be used in aDUV excimer laser lithography or electron beam lithography, andparticularly in a lithography using the ArF excimer laser.

1. (amended) a resist resin capable of being solubilized in an alkalinesolution by the action of an acid, characterized by comprising a monomerunit represented by the following formula (II):

wherein a substituent R³represents an alkyl group, or a functional groupcomprising an acid-deprotectable protecting group, m representing thenumber of R³ is 0 (non-substitution), 1, 2 or more, R³ may be differentfrom one another, provided that m is 2 or more, and n represents aninteger of 0 to
 4. 2. The resist resin according to claim 1,characterized by further comprising a monomer unit having an alicyclicskeleton and a monomer unit having a lactone skeleton (except themonomer unit of Formula (II), the same exception being applied to thefollowing claims).
 3. The resist resin according to claim 2,characterized in that the monomer unit having an alicyclic skeleton isat least one type selected from the group consisting of cyclohexyl(meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate,tricyclodecanyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, andderivatives having the substituent on these alicyclic rings.
 4. Theresist resin according to claim 2 or 3, characterized in that themonomer unit having a lactone skeleton is at least one type selectedfrom the group consisting of (meth)acrylate having a δ-valerolactonering, (meth)acrylate having a δ-butyrolactone ring, and derivativeshaving the substituent on these lactone rings.
 5. The resist resinaccording to claim 2 or 3, characterized in that the monomer unit havinga lactone skeleton is at least one type selected from the groupconsisting of (meth)acrylate having a polycyclic lactone ring andderivatives having the substituent on these polycyclic lactone rings. 6.A chemically amplified resist composition comprising the resist resinaccording to claims 1 to 5 and a photo acid generator.
 7. A method offorming a pattern, comprising a step of applying the chemicallyamplified resist composition according to claim 6 on a substrate to beprocessed, an exposure step and a developing step.
 8. The method offorming a pattern according to claim 7, wherein an exposure source usedin the exposure step is selected from the group consisting of a KrFexcimer laser beam, an ArF excimer laser beam, an F₂ excimer laser beamand an electron beam.